Galvanizing composition and process



May 28, 1957 H. F. MYERS ET AL GALVANIZING COMPOSITION AND PROCESS Filed Oct. 28, 1955 Y IN VEN TORS KENQY F. MVfQS By 0770 A. PROfLSS 7.45m .477'0Q/VE) United States. Patent GALVANIZING COMPOSITION AND PROCESS Henry Ft Myers, Pittsbnrg, and Otto A. Proelss, Antioch, Califi, assignors to United States Steel (Iorporation, a corporation. of New Jersey Application October 28, 1955, Serial No. 543,575

10 Claims. (Cl. 117-109) This invention relates to an improved method and coating composition for galvanizing small ferrous articles in drums, a procedure sometimes known as hotrunriblingfi' The present application is a continuation-impart'bf'ouc co-pending application Serial No. 353,900, filed May 8-,,

1953, and now abandoned.

Commonly small ferrous. articles, su'clias. nails, are galvanized in batch lots by mixing or rumbling them in a heated drum, which. contains a quantity of zinc in molten or flake form along with a flux. The drum is heated to a suflicient temperature and the charge is mixed for a sufiic'ient time for the fluxto react with the surfaces of the articles and for molten zinc to flow over these surfaces and coat them. After being coated, the articles aredumped into a quench. bath or are spray-cooled to set the coating and wash off excess flux. The washed articles then can be drained, dried and packaged. The fluxes commonly used in such processes are ammonium chloride and zinc ammonium chloride.

The quality of articles galvanized by hot rumbling depends on several factors, such as, (a) how well the-surface is cleaned before the articles reach the drums (b the fluxing action, and (c) the skill of the operator, whoiiiust control the relation between quantity of flux, temperature and time of mixing. The prior art has recognized the diffieulty of producing smooth, bright'coated nails, for example, and has used small additions of tin metal, tin-zinc alloy, lead, or tin pot by-products (skimmings or dross) to increase the fluidity of the zinc and produce brighter and smoother coatings.

An object of the present invention is to provide improved hot rumbling galvanizing methods and coating ingredients which minimize galvanizing defects, such as uncoated spots, and produce smoother and brighter coatings than usual methods.

A further object is to provide improved hot rumbling galvanizing methods and coating ingredients which reduce the quantity of zinc required in the bath to deposit a coating of any given weight on the articles.

A further object is to provide an improved method of preparing article surfaces, which method is an integral part of the galvanizing operation and reduces the resistance to flow of coating material.

The single figure of the drawing is a vertical section of a typical conventional apparatus in which our method can be performed. The apparatus includes a rotatable drum 10, a suitably fired furnace 12 in which the drum is journaled, and a drive 13 for the drum. A charge of articles A, together with a galvanizing bath constituted in accordance with our invention, are fed into one end of the drum.

According to our invention volatile tin salts are incorporated in the galvanizing charge along with the zinc and the usual flux. Many tin salts which have appreciable vapor pressure near the melting point of zinc can be used, but with chloride fluxes we prefer the tin chlorides or sodium stannate. Both stannous and stannic chlorides are operable, although stannic chloride is less practical Patented May 28-, 1951 ice . 2. because of excessive. fuming. A composition for galvanizing 1,00 parts by weight of small articles, such as: nails, in accordance with our invention consists of the following:

Zinc 4 to parts by weight.

Flux At least 1 part by weight.

Volatile tin salt Sufficient to furnish a tin content equal to 0.25 to 4.0 percent; of the weight of zinc.

In accordance with known principles,.the quantityof zinc needed within thetoregoin-grange is a function of the total surface area of the articles. Small sized articles which have a large total surface area of course require a greater quantity of. zinc thanlarger articles which have less total surface area.

, zinc reduction is greatest for larger size articles. In a typical operation of galvanizing /8 inch x 11 gauge roofing nails, we have reduced the quantity of. zinc needed for ZQOpon'nds ofnail's from about 25 pounds to about 21.5 pounds, a saving of 14 percent, by adding. tin in an amount equivalent to; 1".25 percent of the weight of zinc.

Specific examples" of charge. compositions for galvaniz-. ihg 200 pounds of inch 1: ll gauge barbed roofing nail's'are as follows:

Example I Pounds Zinc flake 21.5 Zinc ammonium chloride 2 Stannous chloride (anhydrous) 0.45

7 Example; ll Pounds Zinc flake 21.5 Zinc ammonium chloride 2 Stannous chloride (SnCl2-2H2O) 0.51

Example 111 Pounds Zinc flake 21.5 Ammonium chloride 2 Stannous chloride (anhydrous) 0.45

Example IV Pounds Zinc flake 21.5

Ammonium chloride 2 Stannous chloride (SnClz-2H2O) 0.51

Example V Pounds Zinc flake 21.5 Zinc ammonium chloride 2 Sodium stannate 0.63

Example VI Pounds Zinc flake 21.5 Ammonium chloride 2 Sodium stannate 0.63

According to our galvanizing method a quantity of clean ferrous articles, for example 200 pounds of nails, is charged into a drum together with the proper proportions of molten or flake zinc, fluxing agent and volatile tin salt. The drum is rotated and heated to an internal temperature between approximately 1200 and 1650 F.

The quantity of zinc actually needed to meet any particular specification is based on f 2,798,965 r f p (preferably 1400 to 1500 R), which melts the flux,

tin salt and the zinc. The tumbling action brings the molten ingredients into intimate contact with the surfaces of the articles and coats these surfaces uniformly. After about five minutes of tumbling in the heated drum, the articles are discharged to a quench. or spray cooler.

Our method attains the benefits of metallic tin additions to the galvanizing charge and also improves the fluxing or surface preparation of the article. Thus the method minimizes the occurrence of uncoated spots and produces more uniform finishes. Its further advantage of conserving zinc has already been pointed out.

While We have disclosed only certain preferred ways of practicing the invention, it is apparent that other alternatives and equivalents may arise. Therefore we do not wish to be limited by the disclosure set forth, but only by the scope of the appended claims.

We claim:

' 1. A galvanizing charge which consists of the following:

Zinc 4 to 13.5 parts by weight.

Flux At least 1 part by weight. Volatile tin salt Sufficient to furnish a tin content equal to /1% to 4% of the weight of zinc, said salt being selected from the group consisting of stannous chloride and sodium stannate.

2. A galvanizing charge as defined in claim 1 in which said volatile tin salt is stannous chloride.

3. A galvanizing charge as defined in claim 1 in which said volatile tin salt is sodium stannate.

.4. A method of galvanizing small articles comprising mixing them in a heated revolving drum with zinc and a flux and containing in addition a volatile tin salt in an amount suflicient to furnish a tin content equal to 4% to 4% of the weight of zinc, said salt being selected firom the group consisting of stannous chloride and sodium stannate.

5. A method as defined in claim 4 in which said volatile tin saltis stannous chloride.

6. A method as defined in claim 4 in which said volatile tin salt is sodium stannate.

, 4 7. A method of galvanizing small ferrous articles comprising mixing them in a proportion of about parts by weight with a charge which consists of the following:

Zinc 4 to 13.5 parts by weight. Flux At least 1 part by weight. Volatile tin salt Sufficient to furnish a tin content equal to to 4% of the weight of zinc.

and heating said articles and charge to a temperature of 1200 to 1650 F. while continuing the mixing for about five minutes until the articles are completely coated with zinc, said salt being selected from the group consisting of stannous chloride and sodium stannate.

8. A method as defined in claim 7 in which said volatile tin salt is stannous chloride.

9. A method as defined in claim 7 in which said volatile tin salt is sodium stannate.

10. A method of galvanizing small ferrous articles comprising mixing them in a drum in a proportion of about 100 parts by weight with a charge which consists of the following:

Zinc 4 to 13.5 parts by weight.

Flux At least 1 part by Weight.

Stannous chloride Sufficient to furnish a tin content equal to to 4% of the weight of zinc.

the flux being of the group consisting of zinc ammonium chloride and ammonium chloride, and heating said articles and charge to a temperature of 1200 to 1650 F. while rotating said drum for about five minutes until the articles are completely coated with zinc.

References Cited in the file of this patent UNITED STATES PATENTS 933,324 Mowry Sept. 7, 1909 1,029,351 Farnham June 11, 1912 1,133,628 Field et a1. Mar. 30, 1915 1,939,667 Csanyi Dec. 19, 1933 2,501,262 Carhart et al Mar. 21, 1950 FOREIGN PATENTS 386 Great Britain of 1857 

10. A METHOD OF GALVANIZING SMALL FERROUS ARTICLES COMPRISING MIXING THEM IN A DRUM IN A PROPORTION OF ABOUT 100 PARTS BY WEIGHT WITH A CHARGE WHICH CONSISTS OF THE FOLLOWING: 